1. Field of the Invention
The present invention relates to a liquid crystal display apparatus and, in particular, to a liquid crystal display apparatus for turning on and off the liquid crystal molecules by forming an electric field in the direction substantially parallel to the substrate surfaces in order to realize a liquid crystal display apparatus having a superior visual angle characteristic.
2. Description of the Related Art
A liquid crystal display apparatus for turning on and off the liquid crystal molecules by forming an electric field in the direction substantially parallel to the substrate surfaces is also called a transverse electric field drive type liquid crystal display apparatus. In the transverse electric field drive type liquid crystal display apparatus, one of a pair of the substrates holding the liquid crystal has a first electrode and a second electrode, and the electric field is formed from the first electrode toward the second electrode. Such a liquid crystal display apparatus is described in JP-A-7-36058, for example.
The horizontal electric field drive type liquid crystal display apparatus uses a liquid crystal of a horizontal alignment type. The liquid crystal is first aligned in a first direction parallel to the substrate surfaces, and upon application of a voltage thereto, comes to be aligned parallel to the substrate surfaces in a second direction rotated from the first direction. Specifically, upon application of a voltage thereto, the liquid crystal molecules try to be arranged in parallel to the electric field formed between the first and second electrodes. The motion of the liquid crystal molecules occurs in a plane parallel to the substrate surfaces, and therefore the visual angle characteristic is not deteriorated unlike in the TN type liquid crystal, thereby realizing a liquid crystal display apparatus having a wide visual angle characteristic.
JP-A-7-159807 discloses a modification of a transverse electric field drive type liquid crystal display apparatus. In this liquid crystal display apparatus, one of a pair of substrates holding the liquid crystal has a first electrode, and the other substrate has a second electrode. The first and second electrodes are at positions staggered from each other in a direction parallel to the substrate surfaces. In this case, the first and second electrodes extend in narrow strips parallel to each other. The plane containing the first and second electrodes is diagonal to the substrate surfaces to thereby form an oblique electric field. The distance between the first and second electrodes, however, is very large compared with the thickness of the liquid crystal layer, and therefore the plane containing the first and second electrodes can be considered substantially parallel to the substrate surfaces. In this case, too, therefore, a horizontal alignment type of liquid crystal is used, which behaves in the same manner as in the aforementioned case.
JP-A-10-48671 discloses a liquid crystal display apparatus driven by an oblique electric field. A pixel electrode and a common electrode are both formed in the shape of comb. Each of the pixel electrode and the common electrode includes a plurality of linear electrode elements parallel to each other.
In the transverse electric field drive type liquid crystal display apparatus with first and second electrodes formed on one substrate, the electric field is formed from the first electrode toward the second electrode. The strength of the electric field is higher near the substrate having the electrodes and weaker near the substrate having no electrodes. Upon application of a voltage, therefore, the liquid crystal is not uniformly aligned between the first and second substrates, and a disclination may occur within a pixel. Also, in the case where only one of the substrates has electrodes while the other substrate has no electrode, static electricity may stay in the alignment layer of the substrate having no electrode.
In the transverse electric field drive type liquid crystal display apparatus with the first substrate having the first electrode and the second substrate having the second electrode, on the other hand, the problem of static electricity is solved. Actually, however, the electric field is formed obliquely to the substrate surfaces from the first electrode toward the second substrate. As a result, when a voltage is applied, the liquid crystal of horizontal alignment type tilts up obliquely while rotating to set in a position parallel to the electric field. It is difficult for the liquid crystal of horizontal alignment type, however, to tilt up obliquely while rotating. The liquid crystal behavior may thus be disturbed.
Further, the transverse electric field drive type liquid crystal display apparatus is so configured that at least one of the first and second electrodes is formed in a pixel, thereby often leading to a small aperture ratio. In view of this, the electrodes are required to be arranged in a manner capable of realizing bright display with a large aperture ratio.
In an oblique electric field system for driving a liquid crystal by applying different voltages to the electrodes on two substrates making up a liquid crystal panel, once the two substrates are misaligned from each other, the gap between the electrode on one substrate and the electrode on the other substrate changes, thereby posing the problem that the voltage-transmittance characteristic undergoes a change. The accuracy with which the two substrates are attached to each other, therefore, is very strict and a very small manufacturing margin is allowed.
An object of the present invention is to provide a liquid crystal display apparatus of transverse electric field drive type in which the behavior of the liquid crystal can be accurately controlled.
A liquid crystal display apparatus, according to the present invention, comprises first and second opposed substrates, a liquid crystal layer sealed between the first and second substrates, first electrodes formed on the first substrate, and second electrodes formed on the second substrate at positions shifted from the first electrodes in a direction parallel to the substrate surfaces, the liquid crystal of the liquid crystal layer being vertically aligned and the dielectric anisotropy of the liquid crystal being positive.
With this configuration, the first electrode is formed on the first substrate, the second electrode is formed on the second substrate, and the first and second electrodes are arranged at positions shifted from each other in the direction parallel to the substrate surfaces. Therefore, when a voltage is applied between the first electrode and the second electrode, an oblique electric field is formed between the first electrode and the second electrode. The liquid crystal molecules are aligned vertically, and the liquid crystal has a positive dielectric anisotropy. As a consequence, the obliqueness of the electric field causes the liquid crystal molecules to be inclined in the direction parallel to the oblique electric field. As a result, an alignment free of disclination is realized with a voltage applied. The absence of disclination eliminates the portion where elastic energy stays and realizes a lower threshold voltage.
Preferably, the liquid crystal comprises a blended liquid crystal containing at least one of a fluorinated liquid crystal and a cyanic liquid crystal.
The first and second electrodes extend linearly and are elongated at least partially. The first and second electrodes are at least partially parallel to each other.
One of the first and second substrates has a black matrix and a color filter. The electrode of the substrate having the black matrix and the color filter constitute a portion of the black matrix. The black matrix is formed in contact with the substrate. The color filter has a slit formed at the position of the electrode formed by the black matrix.
One of the first and second electrodes is a solid electrode, and the color filter is formed on the transparent solid electrode. The color filter has a slit, and the portion of the solid electrode exposed from the slit constitutes one of the first and second electrodes.
A third electrode is formed on one of the first and second electrodes in such a manner as to share a potential with one of the first and second electrodes.
The third electrode is formed in such a manner as to be overlapped at least partially with one of the first and second electrodes.
One of the first and second substrates has a gate line and a data line, and the electrode formed on the other of the first and second substrates is formed in such a manner as to cover the data line. One of the first and second electrodes is displaced in the direction toward the pixel from the data line in the same plane and covers the data line.
One of the first and second substrates has a gate line and a data line. One of the first and second electrodes is formed in proximity to one of the gate line and the data line.
One of the first and second substrates has a gate line and a data line. The electrode formed in the other of the first and second substrates is formed in a pixel.
One of the first and second substrates has a gate line, a data line and a TFT. One of the first and second electrodes is connected to the source electrode of the TFT and extends onto the next gate line thereby to form an subsidiary capacitor.